1. Field of the Invention
The present invention relates to a method for fabricating a metal ring-fitted optical device, and to the metal ring-fitted optical device. In particular, the invention relates to a method for fabricating a metal ring-fitted optical device, which is applicable to fabrication of an optical device having an optical functional face formed on its both surfaces and having, around its side face, an outer peripheral side part for positioning the device relative to the fixture to which the device is fitted; and relates to the metal ring-fitted optical device.
2. Description of the Related Art
One example of conventional optical devices is shown in FIG. 7 and FIG. 8, in which a small-diameter aspherical lens 70 made of optical glass and having a diameter of, for example, 1 mm or so is fitted to a V-grooved fixture (V-GROOVE) 60. As illustrated, the lens 70 is fitted into the V-groove 64 of the carrier 62 mounted on the stand 61 on which the lens 70 faces the laser diode 63 also mounted on the stand 61. In this structure, it is easy to make the optical axis OD of the laser diode 63 correspond to the optical axis OL of the lens merely by fitting the lens 70 into the V-groove 64 in the carrier 62 provided that the dimensional accuracy of the lens 70 relative to its outer peripheral face 71 is ensured. In that condition, this structure does not require any optical axis alignment control.
In the lens-fitting structure of the illustrated case, the lens 70 is fixed to the carrier 62 with the V-groove 64 formed therein, via an adhesive applied between them. However, using the adhesive 80 for fixing the lens 70 is problematic in that handling the adhesive 80 is troublesome and the component that evaporates from the adhesive 80 may deteriorate the atmosphere around the lens. Accordingly, it is desired to fit the lens to the carrier with solder, not using such an adhesive.
For soldering the lens in the manner as above, the peripheral part of the lens must be previously metallized. For metallizing such small-sized lenses, metal sputtering around lenses may be taken into consideration. However, since the lenses are small-sized, it is difficult to accurately handle them for metallization. In addition, the optical functional faces of the lenses must be protected so as not to be metallized. For these reasons, it has heretofore been impossible to efficiently produce the desired lenses.
To solve the problems, a method has been proposed of forming a solderable, thin-walled metal ring around the peripheral side face of a lens.
The lens of the type is so designed that a glass lens is fitted into a solderable, thin-walled metal ring, and this is therefore solderable. In addition, since its sidewall is covered with a metal ring, the glass lens inside the metal ring is damaged little as compared with nude glass lenses. Moreover, the glass lens fitted in such a thin-walled metal ring is better than a glass lens fitted in a thick-walled lens barrel, since the effective diameter of the metal ring-fitted lens could be almost the same as the outer diameter of the non-protected nude glass lens alone. The metal ring-fitted lens of the type may be fabricated, for example, as follows:
Briefly, a cylindrical mold to define the outer shape of the glass lens to be formed is set in an electromagnetic induction furnace, while the upper and lower pressing molds to be fitted into the cylindrical mold to thereby form the light-entering face and the light-emitting face of the glass lens are in the furnace above and below the cylindrical mold, and a lens material is put into the cavity surrounded by the molds. In that condition, the pressing molds are pressed toward the cylindrical mold to thereby form the intended optical faces of the glass lens while, at the same time, a metal ring is fitted to the side periphery of the lens being molded in that manner.
In this embodiment, a metal ring of which the outer diameter is somewhat smaller than the inner diameter of the cylindrical mold is disposed inside the cylindrical mold, and an optical glass pellet, a type of optical material is put inside the metal ring. With that, the cylindrical mold is heated with the induction current from the coil disposed outside the cylindrical mold so as to soften the glass pellet inside the metal ring at a predetermined temperature, and thereafter the thus-softened glass pellet in the metal ring is pressed by the upper and lower pressing molds to thereby form the lens face of a desired shape, while, at the same time, the metal ring is pressed and expanded by the pressure applied to the glass material toward the cylindrical mold disposed around the metal ring, and then this is cooled. Through the process, a metal ring-fitted lens having a predetermined outer shape is fabricated.
According to the lens fabrication method as above, when the glass material in the metal ring is compressed by the molds that surround it, the metal ring around the glass material expands outside owing to the inner pressure applied thereto and, as a result, it is pressed against the inside wall of the cylindrical mold disposed outside it and the glass material is then solidified as such to thereby have the thus-expanded shape. Thus solidified, therefore, the lens may have the desired shape. The degree of thermal shrinkage to be caused by cooling the glass material and the metal ring can be previously estimated. Accordingly, the lens thus fabricated may have the desired dimension by controlling the size of the cylindrical mold to be used.
In the prior-art fabrication method mentioned above, the pressing molds to press the glass material toward the cylindrical mold do not enter the opening of the metal ring in which the glass material forms a lens. When the glass material is pressed according to this method, all of the pressed glass material could not be completely housed inside the metal ring, and some glass material may be often forced out of the metal ring since the size of the metal ring and that of the glass pellet vary.
As a result, the outer peripheral shape of the lens could not be accurately formed, and even if the thus-fabricated lens is fitted to a fixture part, it could not be disposed in the predetermined site. This is one problem with the method. Another problem with the method is that the excess glass material having been forced out of the metal ring will be broken or cracked and will often damage the surface of the lens.
To solve the problem with the excess glass material forced out of the metal ring, a method may be taken into consideration of forming the lens surface by pressing at least one of the pressing molds into the inside of the metal ring.
In this method, however, the outer diameter of the pressing molds must be smaller than the inner diameter of the metal ring. Therefore, in this method, there will be a space, though narrow, between the pressure mold and the metal ring in the direction of the diameter of the metal ring.
As a result, the glass material being molded will be forced out through the narrow space by the pressing force of the mold and it will form thin flakes having been forced out of the narrow space. The thus forced-out thin flakes form impurities and will be broken to damage the normal face of the lens formed.